If you don`t know how to bench properly and in order to correct your eventual common mistakes to improve muscle growth please read carefully this "How to bench tips and Common Mistakes" post.
Lack of over-all body tightness is one of the mistakes
Keep the bar in line with the wrist and elbows (tip)
Don’t push the bar off you. Push yourself away from the bar to bench better and grow muscle faster
Tighten your back (good how to bench tip, isn`t it? :D)
Get your upper back and core stren...